The present invention relates to machines for removing fluids from between overlapping sheets of material. The present invention relates in particular to removing air from stacks of paper sheets prior to subjecting the sheets to cutting operations.
In the production of many sheet-like products, including paper products, individual products are produced by first making a relatively large sheet, followed by cutting the sheet into individual products. For example, many paper products, such as letter bond, may be produced by making a relatively large sheet of bond paper, followed by cutting the bond into letter or legal-size sheets.
Copending application Ser. No. 07/255,142 (filed Oct. 7, 1988) by Attilio P. Scalzitti, entitled "Method and Apparatus for Removing Fluid from Overlapping Sheets of Material" is herein incorporated by reference.
Similarly, in the printing industry, different items commonly are printed on one large sheet of material in order to facilitate printing and handling. Such items may include brochures, stamps, and labels, for example. Although plastic, metal foil or a variety of other materials may be employed, most printing is performed using some type of cellulose-based material, such as paper, as the surface to which print is applied.
Labels are employed throughout the industrialized world to convey useful information, such as product identity, composition, quantity, source, directions for use and safety information. Products on which labels may be used include food stuffs, cleaning supplies, machine parts, medical supplies, and a plethora of other useful items. Typically, many labels are produced by printing a plurality of labels, often as many as 90, on one sheet of material, followed by cutting the labels apart and applying them individually to containers of products.
Materials such as ink and paper generally constitute a significant cost of the production of any printed matter. It is therefore desirable, when a plurality of items is printed on one sheet of material, that the items be printed as close to each other as possible in order to maximize the number of items on one sheet. It is also desirable to position the items on the sheet so that individual items may be cut apart using a few knife strokes as possible. These objectives are often accomplished by printing items on a sheet so that the edge of one item corresponds to the edge of another, so that the items may be severed by only one cut, without leaving superfluous material in between. However, this technique requires that the sheets be cut with a great deal of precision, such as in the printing of labels on the order of 1/64 inch, as inaccurate cuts outside of acceptable tolerances may cause the printed product to be rejected.
Further, although sheets may be cut individually, it is preferable that more than one sheet be cut at once in order to speed production and lower cost. For example, a typical label production run may involve the printing and cutting of more than 200,000 sheets. It is in part for this reason that identical sheets of labels typically are stacked one upon the other after printing so that multiple sheets may be cut simultaneously. However, in most printing operations this stacking is relatively crude, and the pages or sheets typically require further alignment before they can be properly cut. It is for this reason that sheets, after stacking, are often then passed to a "jogger".
Although a variety of jogging apparatus are known in the art, the typical jogger employs two adjacent edges, typically straight edges at a right angle to each other, and subjects the sheets to relatively abrupt, oscillating motion relative to the edges. This motion causes the sheets in the stack to shift position until they abut the edges, thereby causing the edges of the sheets in the stack to become aligned with each other. Often air is waved between the sheets in the stack during jogging, such as by manually waving or "winding" several sheets at a time, to lessen frictional contact between adjacent sheets and thereby facilitate the sheets shifting position.
Once the sheets have become aligned so that, within acceptable tolerances, items of the same dimensions printed on the sheets are aligned vertically in the stack, the stack is passed to a cutting machine where the stack comes in contact with a knife apparatus, and the individual items are severed from each other. Although it is often relatively easy to accurately cut the top few sheets in a stack, inaccuracies tend to develop as the knife passes through a stack, so that the sheets in the middle or bottom of the stack may be cut so inaccurately that they must be discarded.
Cutting inaccuracies may develop as a result of a variety of factors, such as knife dullness, loss of clamp pressure on the cutter, inadequate jogging, and uneven ink distribution on the sheets. One factor which contributes substantially to cutting inaccuracies is the presence of air or some other fluid between the sheets in a stack, as this usually lessens frictional contact between the sheets and permits them to shift position as the knife advances through the stack. Although inaccuracies in cutting are a problem in the production of many products, including non-printed products like legal or letter-size stationary paper, this problem is particularly acute where cutting of printed labels is concerned due to the fact that many labels may be printed on a single sheet and must be cut with a relatively high degree of accuracy.
At least two techniques have been employed in the printing industry to remove air from between pages in a stack. One such means is a jogger equipped with a roller, wherein the roller passes over the surface of the stack during or after alignment of the sheets. Another device, disclosed by U.S. Pat. No. 4,509,417, FIG. 3., removes air from between sheets in a stack by grasping one end of the stack and pulling the stack through the nip between two rollers.
Although these means may be adequate for some operations wherein a great deal of cutting precision is not required, these methods and equipment for fluid removal may be inadequate for the production of certain products, especially such as labels, brochures and other printed matter, wherein it is imperative that shifting of position of the sheets during cutting be kept to a minimum. As a result, an apparatus and method which effectively remove fluid such as air from overlapping sheets of material so that shifting of sheets during cutting is minimized may offer significant practical advantages over apparatus and methods known in the art.